Why are UV-A rays less harmful than UV-B rays?

UV-A rays are less harmful than UV-B rays because they have a longer wavelength, resulting in less energy and less skin damage.

UV-A and UV-B rays are both types of ultraviolet radiation emitted by the sun. However, they differ in their wavelengths and the extent of damage they can cause to the skin. UV-A rays have a longer wavelength, ranging from 320 to 400 nanometres, compared to UV-B rays which range from 280 to 320 nanometres. The longer the wavelength, the less energy the radiation carries. Therefore, UV-A rays carry less energy than UV-B rays.

The energy carried by UV radiation is a critical factor in determining its potential harm. High-energy radiation, like UV-B rays, can directly damage the DNA in skin cells, leading to skin cancer. UV-B rays are also primarily responsible for sunburns. On the other hand, UV-A rays, with their lower energy, are less likely to cause these immediate and visible forms of skin damage. However, it's important to note that prolonged exposure to UV-A rays can still lead to indirect DNA damage and contribute to skin ageing and potentially cancer.

Furthermore, UV-B rays are more biologically active. This means they have a greater potential to cause biological changes in the skin, such as the production of melanin, the pigment that gives skin its colour and helps protect it from the sun's rays. Overexposure to UV-B rays can lead to an overproduction of melanin, resulting in skin darkening or tanning. In contrast, UV-A rays are less biologically active and therefore less likely to cause these changes.

In summary, while both UV-A and UV-B rays can cause harm to the skin, UV-B rays are generally more harmful due to their shorter wavelength, higher energy, and greater biological activity. However, it's crucial to protect your skin from both types of UV radiation to minimise the risk of skin damage and skin cancer.